In conventional overhead valve internal combustion engines at least two valves reciprocate to provide intermittent communication between intake and exhaust manifolds and a combustion chamber. The valves have valve stems which are commonly disposed in valve stem guides, supporting axial motion in an engine component such as an engine head. Lubrication is provided to upper portions of the valve stems by a spray of lubricating oil within a valve cover disposed over the head, or by gravity flow from an associated rocker arm. Oil flows by the force of gravity and may be encouraged by a pressure differential in the manifold versus crankcase pressure along a free upper end of the valve stem toward the manifolds and valve heads.
Valve guide seals located between the valve stem and the valve guide serve various purposes. First, they minimize engine oil consumption by restricting oil entry into the manifold and the combustion chamber. Second, they help to minimize exhaust particulates which contribute to pollution. Third, they are helpful in minimizing guide wear, which is of particular importance with diesel engines due to the nature of their operation.
Valve stem seals have been commonly located on the upper end of the valve guide. The upper end of the valve guide is distal to the combustion chamber, thereby distancing the seal from the intense heat of the combustion gases. However, despite such heat, the ideal location of a valve stem seal is near the lower end of the valve guide because lubricating oil may then be freely presented to the stem and guide wear surfaces. As a compromise between heat and function, it would be desirable to locate a valve stem seal within the guide, but somewhere above the lower end of the guide where temperature exposure is reduced. Locating a conventional seal in such a location is impossible since it is spaced away from both axial ends of the guide and would be destroyed when the guide is reamed to a final guide bore size, location and finish.